Sealing plugs for closing holes in walls and the like, of the type including an elastic body and a stem such that the elastic body expands radially by pulling on the stem, are known. Such plugs are widely used for sealing holes that are provided for example in a concrete wall due to the manufacturing process. As is well known, concrete walls are manufactured allowing a gap between formwork panels which are arranged facing one another. Said panels are secured to one another by transverse bolts having threaded ends projecting out of the panels to be able to screw the corresponding nuts. Once the panels are secured, the concrete is poured into the gap which is arranged sandwiched between the formwork panels. To prevent the concrete from adhering to the transverse bolts once set, these bolts are usually first covered or placed inside a tube (normally made of plastic) which is sometimes removed when stripping formwork and other times not. Once the concrete has set, the formwork panels are dismantled and the transverse bolts are disassembled. Therefore, once said transverse bolts are disassembled, they create through holes in the concrete wall which must be closed and sealed to prevent water leaks.